Jerry_NJ has a gives a good recommendation in regards to allergy testing. Be warned that allergy testing is just a panel of local allergens and common indoor allergens, so it doesn't include all the things to which you might be allergic. So, looking at all aspects of your life is a good idea, as Jerry_NJ mentioned.
Good luck.
Well 40 is way to young to be your body is just worn out : ) So allergy is a possibility.
Given the symptoms are not constant, I assume the cats are not the problem source.
If the symptoms crop up on a periodic basis I'd look for some activity, environmental, food that "maps" to the period of the symptom. By environmental I mean everything, flowers, trees, gym, visit to the country side, .... and food includes drink but dairy, nuts, grains, protein, shell fish, .are some of the more likely problem areas. I can't list all, as it is all, but your search can progress by elimination.
Of course you can go to a allergist doctor and get the series of tests, check on you insurance first.
If an alergy it may be a tough time finding what the problems are, but again being you have periodic (time) symptoms look real closely at what you were doing in the few days before the symptoms occur.